Stock CIS, CONEHEAD discussion

["Scott M." <scottmo@teleport.com>]

turbo,

I attempted to email you directly, but both of my messages
got bounced back.

>From my previous discussion (or ranting) regarding the
travel of the air flow plate, and the voltage reading I
measured off the potentiometer, you said, 

> The travel of the air flow sensor plate is not linear
just look at the
>shape of the funnel the plate rides in.all of the air goes
around the
>plate and the shape of the funnel regulates the amount of
lift and the amount of fuel.

Yes, yes, yes......you are most certainly correct, the
linear relationship is only between
the movement of the air flow plate and the movement of the
plunger in the fuel distributor. I need to verify if the
resistance change is also linear with the movement of the
air flow plate.

As you indicated, the air flow meter Cone has steeper wall
sections at the bottom and at the top which means when the
plate is located in this steeper section of the cone, for a
given increase in air flow, the air flow plate/fuel plunger
will move higher and provide a richer mixture for off idle
conditions and for full throttle/load conditions. Stated
another way, if the air flow plate was in the middle
section of the cone with a more gradually sloped wall
section there would be less movement of the air flow
plate/fuel plunger for a given increase of air flow.   

Regarding our discussion about whether the stock CIS can
support 300-325 HP, another list member pointed out that
your point of view may be coming from your experience with
"modified" CIS systems that have the control pressure
changed, the frequency valve duty cycle increased, or basic
tweaking of the lower chamber pressures to richen up the
mixture.

My main interest is in finding out the HP / air flow/ fuel
flow limits of  the "stock" CIS system without any
modifications i.e. just the factory settings. In other
words, how far can I push this stock system until I need to
consider more extensive tweaking. I think we may have been
comparing apples and oranges here. 

Another data point, on the bench, I measured voltage output
from the potentiometer that is used on the air flow meter
assembly from a 86-88 5000TQ (Bosch # 0438 121 053, Audi #
034 133 353D) and saw the voltage range from 0-4.75 V. The
later MC engines like the one used in my '89 200TQ's have a
different air flow meter assembly, Bosch # 0 438 121 064,
Audi 034 133 353L) 

I need to compare these two air flow meters to see if the
earlier version has more flow capability or just possibly
uses a different cone shape.

Question for the list:
Has anyone looked into getting a higher flowing air flow
metering assembly/fuel distributor from a different make
vehicle with a large six cylinder engine and adapting this
to work on the highly modified I5 10V Turbo Audis? 

As another listmember pointed out once, the I5 fuel
distributor head is cast from a 6 cylinder unit but has one
port blocked off.

May  the air flow be with you.
Scott M.
ChipFlippinGipper